In the past, there has been known an exhaust gas purification system which is provided with a particulate filter arranged in an exhaust passage of an internal combustion engine, an SCR catalyst arranged in a portion of the exhaust passage at the downstream side of the particulate filter, a reducing agent supply means to add a reducing agent into an exhaust gas flowing into the SCR catalyst, and an EGR mechanism to recirculate a part of the exhaust gas from the exhaust passage to an intake passage. In such an exhaust gas purification system, there has been proposed a technology in which when the temperature of the particulate filter is made to go up for the purpose of oxidation of particulate matter (PM: Particulate Matter) trapped in the particulate filter, the amount of recirculation of EGR gas is made to decrease (see, for example, a first patent literature).
In an exhaust gas purification apparatus which is provided with a particulate filter arranged in an exhaust passage of an internal combustion engine, and an EGR device to recirculate a part (EGR gas) of exhaust gas from the exhaust passage to an intake passage, there has also been proposed a technology in which when the internal combustion engine is in a medium load operating state, the amount of NOx discharged or emitted from the internal combustion engine is decreased by increasing the amount of EGR gas (see, for example, a second patent literature).
In an exhaust gas purification apparatus which is provided with a particulate filter arranged in an exhaust passage of an internal combustion engine, and an EGR device to recirculate a part (EGR gas) of exhaust gas from the exhaust passage to an intake passage, there has also been proposed a technology in which when the temperature of the particulate filter is high and when the concentration of oxygen in the exhaust gas is high, the amount of exhaust gas passing through the particulate filter is decreased by carrying out the processing to increase the amount of EGR gas, etc. (see, for example, a third patent literature).
In an exhaust gas purification apparatus which is provided with an NOx catalyst arranged in an exhaust passage of an internal combustion engine, and an EGR device to recirculate a part (EGR gas) of exhaust gas from the exhaust passage to an intake passage, there has also been proposed a technology in which when the temperature of the NOx catalyst is higher than an active region, an EGR ratio is made large, thereby attaining a decrease in the temperature of the exhaust gas (see, for example, a fourth patent literature).
In an exhaust gas purification apparatus which is provided with a particulate filter arranged in an exhaust passage of an internal combustion engine, a first EGR device to recirculate a part (EGR gas) of exhaust gas from a portion of the exhaust passage at the upstream side of a turbine to a portion of the exhaust passage at the downstream side of a compressor, and a second EGR device to recirculate a part (EGR gas) of exhaust gas from a portion of the exhaust passage at the downstream side of the turbine to a portion of the exhaust passage at the upstream side of the compressor, there has also been proposed a technology in which when the temperature of the exhaust gas is higher than the regeneration temperature of the particulate filter, the EGR gas is recirculated by the use of the second EGR device (see, for example, a fifth patent literature).
In an exhaust gas purification apparatus which is provided with a particulate filter arranged in an exhaust passage of an internal combustion engine, and an NOx catalyst arranged in a portion of the exhaust passage at the downstream side of the particulate filter, there has also been proposed a technology in which regeneration of the particulate filter and denitration of NOx are carried out by adjusting the concentration of oxygen in the exhaust gas (see, for example, a sixth patent literature).